Straits of Mackinac
Geology and history 
The Straits of Mackinac a major shipping lane providing passage for raw materials and finished goods, connecting, for instance, the iron mines of Minnesota to the steel mills of Gary, Indiana. Before the railroads reached Chicago from the east, most immigrants arrived in the Midwest and Great Plains by ships on the Great Lakes. The straits is five miles (8 km) wide at its narrowest point, where it is spanned by the Mackinac Bridge. Before the bridge was built, car ferries transported vehicles across the straits. Today passenger-only ferries carry people to Mackinac Island, which does not permit cars. Visitors can take their vehicles on a car ferry to Bois Blanc Island.
Islands in the Straits of Mackinac include the two populated islands, Bois Blanc and Mackinac, and two that are uninhabited: Round and St. Helena islands. At 11 miles (18 kilometers) in length, Bois Blanc is the largest island in the Straits.
The straits are shallow and narrow enough to freeze over in the winter. Navigation is ensured for year-round shipping to the Lower Great Lakes by the use of icebreakers.
The Straits were an important Native American and fur trade route. Located on the southern side of the Straits is the town of Mackinaw City, Michigan, the site of Fort Michilimackinac, a reconstructed French fort founded in 1715, and on the northern side is St. Ignace, Michigan, site of a French Catholic mission to the Indians, founded in 1671. The eastern end of the Straits was controlled by Fort Mackinac on Mackinac Island, a British colonial and early American military base and fur trade center, founded in 1781.
Straits of Mackinac today 
The Straits are patrolled by a detachment of the United States Coast Guard based at Graham Point, St. Ignace. A shipping channel through the winter ice is maintained by the Coast Guard's Great Lakes icebreaker, USCGC Mackinaw, based in Cheboygan, Michigan near the eastern edge of the Straits. This new vessel went into service during the 2005-06 ice season.
Most of the Straits have been set aside by the U.S. state of Michigan as the Straits of Mackinac Shipwreck Preserve, a riparian public space dedicated to those personnel who were lost aboard the boats and ships that sank in these dangerous shipping lanes.
Lighthouses in the Straits of Mackinac include:
- The McGulpin Point Light, on McGulpin Point, 3 miles (4.8 km) west of Fort Michilimackinac.
- The Old Mackinac Point Light, in Mackinaw City, Michigan, which is open to the public.
- The Round Island Light on Round Island, which is not open to the public but which can be viewed from the Mackinac Island ferry channel.
- The St. Helena Island Lighthouse, which is not open to the public but is visible from a rest area on U.S. Highway 2 at Gros Cap, Michigan west of St. Ignace, Michigan.
- The Bois Blanc Light, which is not open to the public, on the northern shore of Bois Blanc.
See also 
- Straits of Mackinac Shipwreck
- Lighthouses in the Mackinac Strait
- Lighthouses of the Straits of Mackinac